1. Field of the Invention
The present invention relates to an electron beam lithography system for drawing circuit patterns to a wafer and a mask by utilizing the electron beam and particularly to an electron beam lithography system which is just suitable for shortening the drawing time and improving the rate of the apparatus operation.
2. Description of the Related Art
In an electron beam lithography system, an X-Y stage for moving a sample is required to draw a pattern on the entire part of the sample such as wafer and mask because the drawing area of the sample on which a pattern is drawn is larger than the deflection range of electron beam. Moreover, since the drawing by the electron beam is conducted under the vacuum condition, the XY stage must be placed within a vacuum chamber which is called a stage-chamber.
In the electron beam lithography system, two or more vacuum chambers are necessary to realize effective pattern drawing, because the stage chamber has a large volume and longer time will be required until the predetermined degree of vacuum required for drawing by electron beam can be attained from the atmospheric condition. Therefore, in an ordinary electron beam lithography system, the stage chambers maintain the low pressure atmosphere and the other chambers change the atmosphere of sample for the vacuum/atmospheric conditions.
Structure of such electron beam lithography system will be explained with reference to FIGS. 10 and 11.
FIG. 10 is an upper cross-sectional view illustrating an example of structure of an electron beam lithography system of the related art. FIG. 11 is a side cross-sectional view of an electron beam lithography system of FIG. 10.
This example is described in the xe2x80x9cJournal of Vacuum Science and Technology B, Vol. 10, No.6, November/December 1992, P.2759xe2x80x9d and is composed of three vacuum chambers.
In this technology, a sample exchange chamber 12 and an evacuation chamber 20 are also provided in addition to the stage chambers 2a. In the sample exchange chamber 12 provided adjacently to the stage chamber 2a via a vacuum valve 11, two sheets of sample having completed or not completed the drawing are loaded by a loader mechanism consisting of an elevator 14 or the like while the evacuation atmosphere is maintained for the purpose of cross-exchange. The inside of this sample exchange chamber 12 has the structure to accommodate two sheets of sample and this chamber is moved upward and downward for selection of samples.
Moreover, in the evacuation chamber 20 adjacent to the sample exchange chamber 12 via a vacuum valve 13, the work for evacuating the sample to the predetermined degree of vacuum condition from the atmospheric condition with a vacuum pump 22 or the work for returning the sample which has completed the drawing to the atmospheric condition with a leaking valve 21 are conducted.
With employment of such structure, the time required for the work to increase or evacuate the pressure between the vacuum condition and atmospheric condition and for loading of sample can be shortened and thereby the total number of sheets of samples for the drawing process of the electron beam lithography system can be increased.
Next, sample loading profiles will be explained. When a wafer 26 is used as the sample, following two kinds of techniques are proposed to load the sample to the stage chamber 2a from the evacuation chamber 20. One is a direct wafer loading technique to load independently the wafer 26 placed on a top table 5 of the XY stage from the evacuation chamber 20 and the other is a pallet loading technique to load the wafer 26 together with a pallet 18 to the stage chamber 2a from the evacuation chamber 20 by providing a plate type board called the pallet within the evacuation chamber 20 and then placing the wafer 26 on the pallet 18.
In the examples of FIG. 10 and FIG. 11, the wafer 26 is loaded together with the pallet 18, while the wafer 26 is placed on the pallet 18, between the stage chamber 2a and sample exchange chamber 12 using three pallets 18.
However, the in-vacuum loading technique using such pallet 18 has following problems to be solved.
1) A pallet 18 is heavy and loading velocity is lowered.
Namely, a recent pallet 18 is provided with an electrostatic chuck to attract the wafer 26. Since this electrostatic chuck is formed of ceramics which is mainly composed of alumina or the like, it is heavier in several times or several tens of times the weight of the wafer 26. In addition, since the chuck is also provided with a ground pin 6 and a rotation positioning mechanism 8 of the wafer 26, the weight of the pallet 18 reaches, as a result, about 1 kg to 5 kg. Therefore, it is difficult to realize the loading velocity identical to that for independently loading a wafer 26 and it has been considered as a cause for drop of total throughput of the electron beam lithography system.
2) Compatibility among the pallets 18, namely error of warp of the wafer 26 during the holding thereof will give influence on the drawing accuracy.
In other words, an electrostatic chuck attracts the wafer 26 along the chuck surface, however, if a plurality of sheets of pallet 18 are used, differences in shape of attracting surface of electrostatic chuck among each pallet 18 and in mounting positions of structural elements give influence on reproducibility among wafers 26 of alignment accuracy to lower the accuracy.
The technique to load in direct the wafer 26 is capable of taking an adequate measure to such problem. In this technique, throughput can be improved because the sample loading velocity can be improved.
Moreover, since a plurality of pallets are not used, the wafer attracting surface always becomes constant on the XY stage and warp of the wafer due to the difference in the processing shape of attracting surface of each pallet is eliminated, drawing alignment accuracy can also be improved.
However, the technique to load in direct the wafer 26 also has the following problem.
3) Exchange of ground pin 6 lowers the rate of the apparatus operation.
In other words, if unwanted electric field or magnetic field is generated in the area near the trajectory of electron beam in the electron beam lithography system, the electron beam is bent to result in the fault of drawing pattern. Therefore, the sample must be kept within the equal potential. Therefore, the sample surface is maintained in the equal potential by pricking the sample with a stylus type projection called a ground pin 6.
However, in the course of drawing the patterns on many samples, the end point of the ground pin 6 is worn out not to maintain the equal potential. Therefore, the ground pin 6 must be exchanged periodically. Since this ground pin 6 is set on the XY stage, the stage chamber 2a must be set to the atmospheric condition on the occasion of replacing the ground pin. Accordingly, the rate of the apparatus operation may be lowered.
4) It is difficult to remove particles deposited on the electrostatic chuck.
Namely, the wafer 26 must be fixed on the X-Y stage at the time of drawing a pattern, but there is an example that warp of 50 xcexcm or more is generated on the wafer 26 coming to electron beam lithography process. If the wafer 26 warped as explained above is fixed for the drawing purpose, the alignment accuracy will be lowered. Therefore, an electrostatic chuck utilizing the electrostatic attracting phenomenon is used in order to fix such wafer under the good flatness condition.
However, if particles are adhered on the surface of electrostatic chuck, the wafer 26 is deformed to lower, on the contrary, the accuracy. In this case, therefore, the particles must be removed from the surface of chuck. The stage chamber 2a is also required to be set under the atmospheric condition while the particles are removed. Thereby, the rate of the apparatus operation may also be lowered.
The problem to be solved in the electron beam lithography system to load in direct the samples is that the ground pin can be exchanged and particles on the surface of electrostatic chuck for attracting the wafer can be removed only under the condition that the stage chamber is set to the atmospheric condition.
It is therefore an object of the present invention to provide an electron beam lithography system which has solved the problems explained above of the related art and can enhance the rate of the apparatus operation and also improve the productivity without lowering the drawing accuracy.
In view of achieving the object explained above, the electron beam lithography system of the present invention forms the stage upper part, consisting of the electrostatic chuck part to be in contact with a sample on the XY stage and a ground pin part, in the structure which may be unloaded from the XY stage body and thereby allows this stage upper part to be moved to the other chamber of small volume partitioned by the vacuum valve from the stage chamber. Thereby, the cleaning of the electrostatic chuck surface and exchange of ground pin can be performed by taking out the stage upper part from the other chamber, namely without setting the stage chamber of large volume for drawing a pattern with the electron beam to the atmospheric condition.
As the other chamber of small volume, an adjustment chamber provided adjacent to the stage chamber or a sample exchange chamber providing a part to place the stage upper part in addition to the place for setting the sample is newly used. These adjustment chamber and sample exchange chamber are provided with a vacuum pump for evacuation and a leaking valve to return chambers to the atmospheric condition in order to realize adjustment of atmosphere for the vacuum and atmospheric conditions.